Transmission opportunity control method and apparatus

ABSTRACT

An access point sends a first frame. The first frame carries a TXOP handover enforcement THE indication field which is a first value or a second value. The first value instructs a station that has accessed a channel to hand over a held TXOP to the access point, and the second value instructs the station that has accessed the channel to hand over the held TXOP to the access point when a handover condition is satisfied. It can be learned that the STA hands over the held TXOP to the AP. Therefore, the AP may be a TXOP holder through the TXOP handover even if the AP fails to obtain the channel through contention, so that a probability of holding the TXOP by the AP is improved, a probability of scheduling a STA by the AP is improved, and system resource utilization is improved.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of International Application No.PCT/CN2016/107093, filed on Nov. 24, 2016, which claims priority toChinese Patent Application No. 201511003316.7, filed on Dec. 28, 2015.The disclosures of the aforementioned applications are herebyincorporated by reference in their entireties.

TECHNICAL FIELD

This application relates to the communications field, and in particular,to a transmission opportunity control method and an apparatus.

BACKGROUND

Devices in a wireless local area network (Wireless Local Area Network,WLAN) need to contend for a right of use of a channel resource, that is,to be a transmission opportunity (Transmission Opportunity, TXOP)holder. Currently, an access point (Access Point, AP) and a non-accesspoint station (Non-Access Point Station, STA for short) have equalcontention opportunities.

In the 802.11ax to which an OFDMA technology is introduced, the AP mayperform uplink and downlink transmission scheduling for different STAson different time-frequency resources, so as to improve system resourceutilization.

However, when a relatively large quantity of user equipments access anetwork, contention is relatively strong, and therefore a probability ofsuccessfully contending for a channel by the AP is relatively low. Ifthe AP cannot be a TXOP holder, multi-user scheduling transmissioncannot be performed, and consequently resource utilization is difficultto improve.

SUMMARY

This application provides a transmission opportunity control method andan apparatus, so as to improve an opportunity of an AP to be a TXOPholder, and improve resource utilization of a WLAN system.

To achieve the foregoing objective, this application provides thefollowing technical solutions:

A first aspect of this application provides a transmission opportunitycontrol method, including: sending, by an access point, a first frame,where the first frame carries a TXOP handover enforcement THE indicationfield, the THE indication field is a first value or a second value, thefirst value instructs a station that has accessed a channel to hand overa held TXOP to the access point, and the second value instructs thestation that has accessed the channel to hand over the held TXOP to theaccess point when a handover condition is satisfied. In the method inthe first aspect, the STA hands over the TXOP to the AP, so that aprobability of scheduling a STA by the AP is improved, and resourceutilization is improved.

A second aspect of this application provides an access point, including:a first transmitter, configured to send a first frame, where the firstframe carries a TXOP handover enforcement THE indication field, the THEindication field is a first value or a second value, the first valueinstructs a station that has accessed a channel to hand over a held TXOPto the access point, and the second value instructs the station that hasaccessed the channel to hand over the held TXOP to the access point whena handover condition is satisfied.

In an implementation of the first aspect and the second aspect, the THEindication field is the first value, or the THE indication field is thesecond value and the station that has accessed the channel satisfies thehandover condition; and the method further includes: receiving, by theaccess point, a second frame sent by the station that has accessed thechannel, where the second frame instructs to hand over the TXOP to theaccess point.

In another implementation of the first aspect and the second aspect, thehandover condition includes that a time used by the station to obtainthe channel through contention is greater than a handover threshold,where the handover threshold is a contention time that is provided bythe access point for the station and that is used to contend for thechannel, and the handover threshold is determined by the access pointbased on a network status, and is sent to the station.

A third aspect of this application provides a transmission opportunitycontrol method, including: receiving, by an access point, a third frame,where the third frame carries first duration and a TXOP transfer grantTTG field, and the first duration is determined by a station that hasaccessed a channel based on a TXOP held by the station; and when the TTGfield is a third value, sending, by the access point, a fourth frame tothe station that has accessed the channel, where the fourth framecarries second duration, the second duration is determined based on aTXOP requested by the access point, the second duration is longer thanthe first duration, and the TXOP requested by the access point isobtained by extending the TXOP held by the station by a preset time. Inthe method provided in the third aspect, after transmission is completedduring a TXOP 1 held by the STA, the AP can hold a TXOP 2, so thatresource utilization can be improved.

A fourth aspect of this application provides an access point, including:a second receiver, configured to receive a third frame, where the thirdframe carries first duration and a TXOP transfer grant TTG field, andthe first duration is determined by a station that has accessed achannel based on a TXOP held by the station; and a second transmitter,configured to: when the TTG field is a third value, send a fourth frameto the station that has accessed the channel, where the fourth framecarries second duration, the second duration is determined based on aTXOP requested by the access point, the second duration is longer thanthe first duration, and the TXOP requested by the access point isobtained by extending the TXOP held by the station by a preset time.

In an implementation of the third aspect and the fourth aspect, themethod further includes: when the TTG field is a fourth value, sending,by the access point, a fifth frame carrying the first duration.

In an implementation of the third aspect and the fourth aspect, afterthe sending, by the access point, a fourth frame to the station that hasaccessed the channel, the method further includes: holding, by theaccess point, the TXOP requested by the access point.

In an implementation of the third aspect and the fourth aspect, afterthe sending, by the access point, a fourth frame to the station that hasaccessed the channel, the method further includes: receiving, by theaccess point, a contention free end CF-End-X frame sent by the stationthat has accessed the channel, where the CF-End-X frame carries thesecond duration, and the CF-End-X frame is used to indicate that datatransmission of the station that has accessed the channel during thefirst duration ends; and holding, by the access point, the TXOPrequested by the access point.

A fifth aspect of this application provides a transmission opportunitycontrol method, including: receiving, by a station, a first frame sentby an access point, where the first frame carries a TXOP handoverenforcement THE indication field; and when the THE indication field is afirst value, sending, by the station, a second frame to the accesspoint, where information of the second frame instructs to hand over aTXOP to the access point.

A sixth aspect of this application provides a station, including: athird receiver, configured to receive a first frame sent by an accesspoint, where the first frame carries a TXOP handover enforcement THEindication field; and a third transmitter, configured to: when the THEindication field is a first value, send a second frame to the accesspoint, where information of the second frame instructs to hand over aTXOP to the access point.

In an implementation of the fifth aspect and the sixth aspect, themethod further includes: when the THE indication field is a secondvalue, determining, by the station, whether a handover condition issatisfied, and if the handover condition is satisfied, sending, by thestation, the Second frame to the access point.

In an implementation of the fifth aspect and the sixth aspect, thehandover condition includes:

a time used by the station to obtain the channel through contention isgreater than a handover threshold, where the handover threshold is acontention time that is provided by the access point for the station andthat is used to contend for the channel.

A seventh aspect of this application provides a transmission opportunitycontrol method, including: sending, by a station, a third frame to anaccess point, where the third frame carries first duration and a TTGfield, the first duration is determined by the station based on a TXOPheld by the station, the TTG field is a third value or a fourth value,the third value is used to indicate that TXOP handover is allowed, andthe fourth value is used to indicate that TXOP handover is not allowed;and receiving, by the station, a fourth frame or a fifth frame sent bythe access point, where the fourth frame carries second duration, thesecond duration is determined based on a TXOP requested by the accesspoint, the second duration is longer than the first duration, the TXOPrequested by the access point is obtained by extending the TXOP held bythe station by a preset time, and the fifth frame carries the firstduration.

An eighth aspect of this application provides a station, including: afourth transmitter, configured to send a third frame to an access point,where the third frame carries first duration and a TTG field, the firstduration is determined by the station based on a TXOP held by thestation, the TTG field is a third value or a fourth value, the thirdvalue is used to indicate that TXOP handover is allowed, and the fourthvalue is used to indicate that TXOP handover is not allowed; and afourth receiver, configured to receive a fourth frame or a fifth framesent by the access point, where the fourth frame carries secondduration, the second duration is determined based on a TXOP requested bythe access point, the second duration is longer than the first duration,the TXOP requested by the access point is obtained by extending the TXOPheld by the station by a preset time, and the fifth frame carries thefirst duration.

In an implementation of the seventh aspect and the eighth aspect, thereceiving, by the station, a fourth frame or a fifth frame sent by theaccess point includes: when the TTG field is the third value, receiving,by the station, the fourth frame sent by the access point; or when theTTG field is the fourth value, receiving, by the station, the fifthframe sent by the access point.

In an implementation of the seventh aspect and the eighth aspect, thesending, by a station, a third frame to an access point, where the thirdframe carries first duration and a TTG field includes: sending, by thestation, a last frame in the TXOP held by the station to the accesspoint, where the last frame carries the first duration and the TTGfield. The TTG field is carried in the last frame, to help the STAcomplete transmission of the STA, and a third-party STA is in an awakestate when the AP holds the TXOP.

In an implementation of the seventh aspect and the eighth aspect, thesending, by a station, a third frame includes: sending, by the station,a contention free end CF-End-X frame, where the CF-End-X frame carriesthe second duration, and the CF-End-X frame is used to indicate thatdata transmission of the station at the TXOP held by the station ends.The CF-End-X frame helps determine TXOP handover, and avoid atransmission fault.

BRIEF DESCRIPTION OF DRAWINGS

To describe the technical solutions in the embodiments of the presentinvention more clearly, the following briefly describes the accompanyingdrawings required for describing the embodiments. Apparently, theaccompanying drawings in the following description show some embodimentsof the present invention, and a person of ordinary skill in the art maystill derive other drawings from these accompanying drawings withoutcreative efforts.

FIG. 1 is a schematic diagram of a WLAN deployment scenario;

FIG. 2 is a flowchart of a transmission opportunity control methodaccording to an embodiment of this application;

FIG. 3 is a flowchart of accessing a channel and sending data by a STAin the 802.11 standard;

FIG. 4 is a schematic diagram of frame interaction in the method shownin FIG. 2;

FIG. 5 is a flowchart of another transmission opportunity control methodaccording to an embodiment of this application;

FIG. 6 is a schematic diagram of frame interaction in the method shownin FIG. 5;

FIG. 7 is a flowchart of another transmission opportunity control methodaccording to an embodiment of this application;

FIG. 8 is a schematic diagram of frame interaction in the method shownin FIG. 7; and

FIG. 9 is a schematic structural diagram of an access point according toan embodiment of this application.

DESCRIPTION OF EMBODIMENTS

FIG. 1 is a schematic diagram of a WLAN deployment scenario. Both an APand a STA need to be a TXOP holder through contention. A purpose of atransmission opportunity control method provided in the embodiments ofthe present invention is to increase an opportunity for holding a TXOPby the AP, so that the AP has more opportunities to schedule each STA,and resource utilization is improved.

The following describes the technical solutions in the embodiments ofthe present invention with reference to the accompanying drawings in theembodiments of the present invention.

FIG. 2 is a transmission opportunity control method, including thefollowing steps:

S201. An AP sends a first frame carrying a TXOP handover enforcement(TXOP Handover Enforcement, THE) indication field.

In some embodiments, the first frame may be a beacon frame (Beacon).Further, the AP may send the beacon frame carrying the THE indicationfield to a STA within a beacon frame interval (Beacon Interval), wherethe beacon frame instructs the STA in the beacon frame interval to handover a TXOP.

In some embodiments, a value of the THE indication field is a firstvalue or a second value. The first value (for example, 1) instructs aSTA that has accessed a channel to hand over a held TXOP to the AP, andthe second value (for example, 0) instructs the STA that has accessedthe channel to hand over the held TXOP to the AP when a handovercondition is satisfied. That is, the first value instructs the STA tohand over the TXOP unconditionally, and the second value instructs theSTA to determine, based on a condition, whether to hand over the TXOP.The AP may set a value of the THE indication field based on arequirement and a network status. For example, if a quantity of accessedSTAs is greater than a preset value, and the AP needs to schedule aplurality of STAs, the AP may set the THE indication field to the firstvalue.

S202. A STA successfully accesses a channel after completing backoff,and records a time used from starting the backoff to completing thebackoff.

FIG. 3 is a flowchart in which a STA starts backoff after sensing achannel, completes the backoff, accesses the channel, and sends data inthe current 802.11 standard series. Specifically, after the STA sensesthat the channel is continuously in an idle state in a distributedinter-frame spacing (Distributed Inter Frame Space, DIFS) (DIFS=34 μs),the STA starts to randomly back off. The STA randomly selects a backoffwindow. The backoff window is an integer multiple of a basic timewindow: a Timeslot (aTimeslot=9 μs), and a minimum of the backoff windowmay be 0. If a time in which the channel remains idle exceeds aTimeslot, the backoff window is decreased by 1. If it finds that thechannel is busy, the backoff is suspended until the channel is idleagain. When the backoff window is decreased to 0, contention succeeds,and data is sent.

S203. The STA parses a value of the THE indication field after receivingthe first frame, and if the THE indication field is a first value, S204is performed, or if the THE indication field is a second value, S205 isperformed.

It should be noted that S201 needs to be performed before S203 in thisembodiment, but an execution sequence between S201 and S202 and anexecution sequence between S202 and S203 are not limited to the sequenceshown in FIG. 2.

S204. The STA sends a second frame to the AP, where the second frameinstructs to hand over a TXOP to the AP.

S205. The STA determines whether a handover condition is satisfied, andif the handover condition is satisfied, S206 is performed, or if thehandover condition is not satisfied, S207 is performed.

In some embodiments, the handover condition is that a time used by theSTA to obtain the channel through contention is greater than a handoverthreshold. The handover threshold is a contention time that is providedby the access point for the station and that is used to contend for thechannel. STAs may contend for the channel within the contention time,and cannot contend for the channel after the time expires. For example,the handover threshold is an average value of time periods used by theSTA in previous five times of channel contention.

In some embodiments, the AP may determine the handover threshold basedon a network status. For example, a network load amount, a quantity ofaccessed STAs, an average quantity of times of backoff collision betweenstations, or the like may be used as a basis for determining thehandover threshold by the AP. Further, the AP may further adjust a valueof the handover threshold based on a value of the network status.

In some embodiments, the handover threshold may be carried in amanagement frame, a control frame, or a data frame sent by the AP to theSTA.

S206. The STA sends a second frame to the AP, where the second frameinstructs to hand over the TXOP to the AP.

In some embodiments, the second frame in this embodiment may be amanagement frame, a control frame, or a data frame that carries TXOPhandover information, or may be a newly defined frame different fromthat in the prior art.

S207. The STA continues to hold the current TXOP.

S208. The AP obtains a TXOP holding right, and performs downlinkmulti-STA data transmission, sends a trigger frame to trigger a randomaccess, performs uplink multi-STA transmission, or the like at the TXOP.

FIG. 4 is a schematic diagram of frame interaction in the method shownin FIG. 2. After receiving the second frame, the AP may further feedback an ACK to the STA. In addition to a function that has been definedin the prior art, the ACK in this embodiment is further used to notifythe STA that the AP starts to hold the TXOP.

It can be learned that in the method in this embodiment, the STA canhand over the held TXOP to the AP, and therefore the AP can be a TXOPholder through the TXOP handover even if the AP fails to obtain thechannel through contention. Therefore, a probability of holding a TXOPby the AP is improved, a probability of scheduling a STA by the AP isimproved, and system resource utilization is improved.

FIG. 5 is another transmission opportunity control method according toan embodiment of this application. A difference from the method shown inFIG. 4 is that after a STA completes holding of a TXOP 1, an AP can holda TXOP 2, and the new TXOP holder may break through a limit of anoriginal TXOP length.

The method shown in FIG. 5 includes the following steps.

S501. After a STA successfully accesses a channel, the STA sends a thirdframe to an AP, where the third frame carries first duration and a TXOPtransfer grant (TXOP Transfer Grant, TTG) field.

The first duration is determined by the STA based on a TXOP held by theSTA. Specifically, a network allocation vector (Network AllocationVector, NAV) in the third frame is set to the first duration. For aspecific manner of setting the NAV, refer to the prior art. Details arenot described herein.

In some embodiments, the TTG field is a third value or a fourth value.The third value (for example, 1) is used to indicate that TXOP handoveris allowed, and the fourth value (for example, 0) is used to indicatethat TXOP handover is not allowed. The STA may set a value of the TTGfield based on a requirement. A bit size occupied by the TTG field maybe determined based on an actual requirement. In this embodiment, toreduce resource overheads, the TTG field is defined as 1 bit.

S502. The AP parses a value of the TTG field, and if the TTG field is athird value, S503 is performed, or if the TTG field is a fourth value,S504 is performed.

S503. The AP sends a fourth frame to the STA that has accessed thechannel, where the fourth frame carries second duration, and the secondduration is longer than the first duration.

The second duration is determined based on a TXOP requested by the AP.The TXOP requested by the AP is obtained by extending the TXOP held bythe STA by a preset time. Specifically, an NAV in the fourth frame isset to the second duration.

S504. The AP sends a fifth frame to the STA that has accessed thechannel, where the fifth frame carries the first duration.

S505. The STA sends a contention free end (Contention Free End,CF-End-X) frame to the AP, where the CF-End-X frame carries the secondduration, and the CF-End-X frame is used to indicate that datatransmission of the STA at a TXOP 1 ends.

A purpose of S505 is to notify the AP that transmission of the STA atthe TXOP 1 ends, and the AP may start to hold a TXOP 2. Therefore, acommunication conflict can be avoided.

S506. The AP holds a requested TXOP 2.

S507 (not shown in FIG. 5). A third-party device (for example, anotherSTA) that can identify a TTG field listens to a frame exchanged betweenthe AP and the STA, and before listening and detecting a frame thatcarries TTG=1, the third-party device sets an NAV of the third-partydevice based on relatively long duration, so that the third-party devicekeeps silent during duration corresponding to the NAV. Once thethird-party device listens and detects the frame that carries TTG=1, itindicates that the AP starts to hold the TXOP 2, and the third-partydevice stops being silent, and prepares to cooperate with the AP inscheduling.

A third-party device that cannot identify a TTG field directly sets anNAV of the third-party device based on relatively long duration.

The following is described with an example based on the foregoingprocess. As shown in FIG. 6, after successfully accessing the channel,the STA sends a control frame, a data frame, or a management frame tothe AP at the TXOP 1, and TTG=1 may be carried in any one of theforegoing frames. Optionally, to ensure that the STA can completetransmission, and the third-party STA that can identify a TTG fieldstops being silent at the TXOP 2, so as to facilitate scheduling by theAP, the AP needs to perform, at a moment close to an end of the TXOP 1as much as possible, duration setting to extend the TXOP 1 to the TXOP2, so that the third-party STA correctly understands that the TXOP 2 isextension of the TXOP 1, and needs to keep awake at the TXOP 2.Therefore, as shown in FIG. 6, TTG=1 is carried in a last frame (data ofa deep color) sent by the STA to the AP. That is, in the last frame sentby the STA to the AP, a value of a TTG field is 1, and an NAV is thesecond duration. In another frame sent by the STA to the AP, TTG=0, or aTTG field is carried, and an NAV is the first duration.

If a frame received by the AP carries TTG=0, the AP sends a feedbackframe to the STA according to a rule of an existing standard. Forexample, a CTS is fed back after an RTS is received, where an NAV is thefirst duration. If a frame received by the AP carries TTG=1, an NAV in aframe fed back by the AP to the STA is the second duration. Afterfeeding back the frame that carries the second duration, the AP holdsthe TXOP 2. The AP may determine a length of the TXOP 2 based on astatus of the AP and a status of a whole BSS.

It can be learned that in the method in this embodiment, after the STAcompletes transmission at the TXOP 1, a resource is not released, but aTXOP 1 holding right is released, so that the AP is a holder of the TXOP2, and continues to access the resource. Therefore, the AP does not needto contend for a channel again, a probability of scheduling a STA by theAP can be improved, and resource utilization can be improved.

FIG. 7 is another transmission opportunity control method according toan embodiment, and the method includes the following steps:

S701. After successfully contending for a channel, a STA sends a sixthframe to an AP at a TXOP 1, where the sixth frame carries firstduration.

S702. The AP sends a seventh frame to the STA, where the seventh framecarries second duration.

S703. The STA sends an eighth frame to the AP, where the eighth framecarries the second duration and a TTG field, and the TTG field is 1.

S704. The AP holds a TXOP 2.

For example, as shown in FIG. 8, the STA sends an RTS. For a specificform of the RTS, refer to the prior art. The AP replies with a CTS. Adifference from a CTS defined in the prior art is that the CTS carriesthe second duration. Last data sent by the STA carries TTG=1, and the APstarts to hold the TXOP 2.

In the method in this embodiment, resource utilization of a WLAN systemcan be improved.

FIG. 9 is a schematic structural diagram of an access point shown inFIG. 2, and the access point includes a first transmitter, a firstprocessor, and a first receiver.

The first transmitter is configured to send a first frame, the firstreceiver is configured to receive a second frame sent by a station thathas accessed a channel, and the first processor is configured to:determine a handover threshold based on a network status, and send thehandover threshold to the station. For specific forms of the first frameand the second frame, a specific function implementation of the accesspoint, and the like, refer to FIG. 2.

A structure of an access point shown in FIG. 5 includes a secondreceiver, a second transmitter, and a second processor. The secondreceiver is configured to receive a third frame. The second transmitteris configured to: when a TTG field is a third value, send a fourth frameto a station that has accessed a channel; and when the TTG field is afourth value, send a fifth frame to the station that has accessed thechannel. The second processor is configured to: after the secondtransmitter sends the fourth frame to the station that has accessed thechannel, hold a TXOP requested by the access point.

In this embodiment, for some forms of the third frame, the fourth frame,and the fifth frame and a function implementation procedure of theaccess point, refer to FIG. 5. Details are not described herein.

A structure of a station shown in FIG. 2 includes a third receiver, athird transmitter, and a third processor. The third receiver isconfigured to receive a first frame, the third transmitter is configuredto send a second frame, and the third processor is configured to:implement a determining process, and hold a current TXOP.

A structure of a station shown in FIG. 5 includes a fourth transmitterand a fourth receiver. The fourth transmitter is configured to send athird frame and a CF-End-X, and the fourth receiver is configured toreceive a fourth frame or a fifth frame.

An access point shown in FIG. 7 includes a fifth receiver, a fifthtransmitter, and a fifth processor. The fifth receiver is configured toreceive a sixth frame and an eighth frame, the fifth transmitter isconfigured to send a seventh frame, and the fifth processor isconfigured to hold a TXOP 2. A station shown in FIG. 7 includes a sixthtransmitter and a sixth receiver. The sixth transmitter is configured tosend the sixth frame and the eighth frame, and the sixth receiver isconfigured to receive the seventh frame.

The foregoing access point and station can implement a change of a TXOPholder from the station to the access point through frame interaction,so as to improve a probability of scheduling a STA by the access point,and improve resource utilization.

The embodiments in the present disclosure are all described in aprogressive manner, for same or similar parts in the embodiments,reference may be made to these embodiments, and each embodiment focuseson a difference from other embodiments.

What is claimed is:
 1. A transmission opportunity control method,comprising: generating by an access point, a first frame, wherein thefirst frame carries a TXOP handover enforcement (THE) indication field,the THE indication field is a first value or a second value, the firstvalue instructing a station that has accessed a channel to hand over aheld TXOP to the access point, and the second value instructing thestation that has accessed the channel to hand over the held TXOP to theaccess point when a handover condition is satisfied; sending the firstframe.
 2. The method according to claim 1, wherein the THE indicationfield is the first value, or the THE indication field is the secondvalue and the station that has accessed the channel satisfies thehandover condition; and, wherein the method further comprises:receiving, by the access point, a second frame sent by the station thathas accessed the channel, wherein the second frame instructing to handover the TXOP to the access point.
 3. The method according to claim 1,wherein the handover condition comprises: a time used by the station toobtain the channel through contention is greater than a handoverthreshold, wherein the handover threshold is a contention time providedby the access point for the station to contend for the channel; and themethod further comprises: determining, by the access point, the handoverthreshold based on a network status, and sending the handover thresholdto the station.
 4. A transmission opportunity control method,comprising: receiving, by a station, a first frame sent by an accesspoint, wherein the first frame carries a TXOP handover enforcement THEindication field; and when the THE indication field is a first value,sending, by the station, a second frame to the access point, whereininformation of the second frame instructing to hand over a TXOP to theaccess point.
 5. The method according to claim 4, further comprising:when the THE indication field is a second value, determining, by thestation, whether a handover condition is satisfied, and if the handovercondition is satisfied, sending, by the station, the second frame to theaccess point.
 6. The method according to claim 5, wherein the handovercondition comprises: a time used by the station to obtain a channelthrough contention is greater than a handover threshold, wherein thehandover threshold is a contention time provided by the access point forthe station and to contend for the channel.
 7. An access point,comprising: a first transmitter, configured to send a first frame,wherein the first frame carries a TXOP handover enforcement THEindication field, the THE indication field is a first value or a secondvalue, the first value is instructing a station that has accessed achannel to hand over a held TXOP to the access point, and the secondvalue instructing the station that has accessed the channel to hand overthe held TXOP to the access point when a handover condition issatisfied.
 8. The access point according to claim 7, wherein the firsttransmitter is configured to send the first frame, wherein the THEindication field is the first value, or the THE indication field is thesecond value and the station that has accessed the channel satisfies thehandover condition; and the access point further comprises: a firstreceiver, configured to receive a second frame sent by the station thathas accessed the channel, wherein the second frame instructing to handover the TXOP to the access point.
 9. The access point according toclaim 7, wherein the handover condition comprises: a time used by thestation to obtain the channel through contention is greater than ahandover threshold, wherein the handover threshold is a contention timethat is provided by the access point for the station and that is used tocontend for the channel; and the access point further comprises: a firstprocessor, configured to: determine the handover threshold based on anetwork status, and send the handover threshold to the station.